I feel you were slightly remiss in not pointing out that Preview.app is more than capable of outputting screen captures, whether .tiff, .pdf, or .pict from the clipboard, in a wide range of formats via the Export... option in the File menu.

For the casual user this is more than sufficient and this oversight, along with the lack of mention of the ctrl + space shortcuts provided by the built in facility, lent this article the unseemly air of an unmarked 'advertorial'.